Yes, Online Maps uses Mercator projection.

Theoretically, it is possible to change the projection type to another, which also uses latitude and longitude. To do this, create a new class that inherits OnlineMapsProjection class, and specify the projection in the map type.
http://infinity-code.com/doxygen/online … ction.html
http://infinity-code.com/doxygen/online … 1ef1b24402

But this does not mean that you can implement any projection.
The possibility of implementing each projection needs to be tested.

i want to use Online Maps for a mmorpg.

But i need a chunk system to recognice when a player entered a new chunk for loading the entitys. And that heavily depends on the map projection ( Mercator stretches the chunks which is bad ).
Does online maps use a mercator projection ? Is it possible to change this type of projection ?